This repository is a monorepo for Microsoft's SQL Server extensions for Visual Studio Code, primarily the `ms-mssql.mssql` extension. It provides a comprehensive suite of database development tools including connection management, object explorer, query execution with rich result grids, schema and table designers, execution plan visualization, schema comparison, database project management (SQL projects, DACPAC), deployment wizards (local containers, Azure SQL, Fabric), backup/restore, and GitHub Copilot integration for natural language querying and schema exploration. The extension follows a client-server architecture where the VS Code extension communicates with a SQL Tools Service (STS) backend via JSON-RPC for language services, metadata, and query execution. The UI is built with React and Fluent UI components rendered in webviews, with state management using a reducer/action pattern over RPC. The monorepo also includes supporting packages: an extension-toolkit providing DI, telemetry, and localization primitives; a performance testing harness (perftest) for measuring extension latency; and companion extensions for data-workspace and database-management-keymap. The codebase demonstrates strong engineering practices with extensive unit and e2e tests, custom ESLint rules, localization infrastructure, and CI/CD pipelines.